Essentially, it pinpoints the number of years an adult can be working at their peak -- before learning gaps or health issues slow them down. The results don't just tell us who is working at their peak, they can also give us some reflections about how governments can help their citizens reach their individual potential, which in turn helps a country's economic output.

What is human capital?

In order to measure the idea of "human capital," researchers started with a base number: 45. That's the highest possible value, meaning a person was working at peak productivity from the second they turned 20 to their hypothetical retirement at the end of 64. In other words, basically impossible.

They then adjusted for education and health by creating values from test scores and the prevalence of common diseases.

"We estimated educational attainment using 2,522 censuses and household surveys; we based learning estimates on 1,894 tests among school-aged children," the study's abstract reads. "And we based functional health status on the prevalence of seven health conditions, which were taken from the Global Burden of Diseases, Injuries, and Risk Factors Study 2016."

The result is a number, lower than 45 but higher than zero, that estimates in years a person's peak productivity.

What the results reveal

According to 2016 data, the top rankers in terms of human capital were Finland, with 28 years; Iceland, Denmark and the Netherlands with 27; and Taiwan and South Korea with 26. The bottom rankers were Niger, Chad and South Sudan, all with three expected years of human capital.

Of the 195 countries tested, the United States clocked in at 27th, with 23 expected years of human capital. However, in 1990, the United States ranked sixth in the world. Curiously, the number of years of human capital expected of a US citizen in 1990 was 22 -- one year less than the current expectation.

So why the precipitous fall? The institute characterizes it as a stagnation "due in part to a lack of improvement in years of education attained."

Why the results matter

According to the institute, "human capital" is an indicator of economic growth or decline. "The World Bank has called for measurement and annual reporting of human capital to track and motivate investments in health and education and enhance productivity," the study claims
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The level of human capital is also a reflection of how much a country invests in its citizens' education and health care.

"Our findings show the association -- between investments in education and health and improved human capital and GDP -- that policymakers ignore at their own peril," institute Director Dr. Christopher Murray said in a release
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